Management Settings page - API Users - minor UI issue

**Short Description:**
If you try to create two API Users with the same name, then the an empty row is being added to the table. Reloading the page fixes that issue.

Steps to reproduce:
> 1. Open the page with PolyDeploy module in edit mode
> 2. Navigate to the `Manage` page from the ActionMenu
> 3. Add a user with the name `TestUser` (this generates the keys)
> 4. Try to add a user with the same name `TestUser`.

Outcome: **Minor UI bug**
> An empty row is added to the [API Users] table because the angular controller is adding an empty [API User] when the database fails to add other API Users with existing names due to a database constraint.

**Workaround**:
> Refreshing the page removes the empty row,